Friday, July 07, 2017

The 2017 Avian Influenza Half-Time Report

OIE Map of HPAI Outbreaks - Jan1st-June 30th 2017


Although the low resolution of the map above doesn't do it justice, over the past 6 months the world has seen its largest expansion of HPAI and LPAI viruses on record.  While the Western Hemisphere and Australia & New Zealand have come away relatively unscathed, the same cannot be said for Europe, Asia, and Africa.
Halfway through 2017 - and at a time when bird flu activity traditional reaches its yearly low point - is a good time to look back at the events of the last 6 months, and see how this year's bird flu activity compares to previous years. 
After jumping from Southeast Asia in 2004, and spreading to 60+ countries in Europe, Africa, and the Middle East by 2007, H5N1 - the only HPAI virus of genuine concern until 2014 - began a slow retreat.
By 2012 it had pulled back from all but about a dozen countries, including Egypt, Vietnam, China, and Indonesia.
In the spring of 2013 another bird flu threat - a Low Path H7N9 virus - emerged in China, but HPAI H5 languished in growing obscurity.  A look at the HPAI (not including LPAI H7N9) activity during the first half of 2013  (see below) tells the tale.

OIE Map - HPAI Jan- June 2013

This nadir would be reversed in 2014 with the emergence of a new, virulent H5N8 virus in South Korea, a new H5N6 virus in China, Laos, and Vietnam, and the return of H5N1 to West Africa.   A snapshot of the first half of 2014 is shown below.

OIE Map - HPAI Jan- June 2014

The following winter, HPAI H5N8 would make it to Europe and North America, H5N1 would spread further in Africa and spark its largest human outbreak on record in Egypt, and several new reassortant viruses (H5N1, H5N2, H5N3) would spin off from the H5N8 virus in both North America and Taiwan.

OIE Map - HPAI Jan- June 2015

While the winter and spring of 2016 saw a pullback, and H5N8 failed to return to Europe or North America, the H5N8 virus reassorted over the summer (see EID Journal: Reassorted HPAI H5N8 Clade - Germany 2016) into a more virulent strain, which sparked the largest avian epizootic in Europe's history when it returned last winter. 
Credit Defra
HPAI H5N8 also spun off new reassortants across Europe, including H5N9, H5N6, and H5N5.  Further afield, HPAI H5N8 made huge inroads over the winter into the Middle East, West Africa, and most recently into the southern half of Africa (Zimbabwe, South Africa).
Meanwhile, in Asia, HPAI H5N6 finally made the jump out of China into North Korea, Japan, and Taiwan, sparking hundreds of outbreaks (mostly in Korea), while evolving into multiple new genotypes. 
While we've seen a remarkable lack of human H5 infections this year, HPAI H5's comeback from near extinction 5 years ago is nothing short of remarkable. Now, instead of one HPAI H5 subtype of concern, we have at least four (H5N1, H5N8, H5N6, H5N5) - with each evolving along multiple pathways.
In any other year, all of that would make for a banner year.  But we aren't even half done with the first half of 2017.
Much like the decline we saw in H5N1 until 2014, China's LPAI H7N9 virus appeared to be lagging after its 4th epidemic wave.  It hit its high point in 2014, and showed declines in both winter waves that followed (see FAO chart below).

That is, until this year, when it has almost equaled the number of cases reported from the first four waves combined.  Not only have the number of cases increased, so has the geographic range of the virus. 

FAO 5th Wave Map - June 28th

Perhaps of even greater concern, the H7N9 virus has evolved into two separate lineages, and an HPAI variant has emerged, and has begun spreading across China (see map below).

The CDC's IRAT system now ranks the newly emerged Yangtze River Delta lineage as being slightly more worrying than the original Pearl River Delta Lineage (see Updating the CDC's IRAT (Influenza Risk Assessment Tool) Rankings), although both are atop their list of viruses with pandemic potential.
We know far less about the threat posed by the HPAI H7N9 version, although two recent studies (see here and here) hint that it may eventually pose an even greater threat to human health.
The $64 question - at least this week - is what this HPAI H7N9 virus will do, and how far it will spread. It was reported less than 100 km from the Russian border two weeks ago, and it appears to be spreading via migratory birds.

The migratory bird flyways which funneled H5N1, H5N8, and H5N6 out of China could potentially do the same someday with HPAI H7N9. While that may not happen for years (if at all), China's neighbors aren't betting against it (see China's Nervous Neighbors).

What happens with avian influenza viruses during the summer months when migratory birds hunker down in their Arctic roosting areas is largely unmonitored. Viruses are swapped, mutations occur, and there are invariably evolutionary winners and losers.

As detailed in Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1, our first clue of what happened during influenza's summer vacation usually comes when migratory birds return in the fall.
For North America and Europe, that usually starts in October. 
The unpredictability of influenza is such that we can't really say what it will do this fall and winter, even with the track record of the last six months to go on. The bird flu rollercoaster ride of the past 5 years shows that these viruses often zig when we expect them to zag. 
About the only thing we can really count on, is that these novel viruses will continue to surprise, and we need to be ready for when those surprises turn into serious global health threats (see World Bank: World Ill-Prepared For A Pandemic).

For more on pandemic preparedness, you may wish to revisit:

HHS Pandemic Influenza Plan - 2017 Update 
OpenWHO: Preparedness Training For Epidemics, Pandemics & Health Emergencies
Are We Prepared to Help Low-Resource Populations Mitigate a Severe Pandemic?
Community Pandemic Mitigation's Primary Goal : Flattening The Curve

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